Laminated structure and method



2 Sheets-Sheet l Nov. 18, 1947. E. l.; VIDAL ETAL LAMINATED STRUCTUREvAND METHOD original Filed sept. 12, 1940 INVENTORS ATTORNEY` Nov. 18,1947. E. L. VIDALV ET Al.

LAMINATED STRUCTURE AND METHOD Original Filed Sept. l2, 1940 2Sheets-Sheet 2 I fz FIG@ @0 INVENTOR l i. #A4417 Ma( BY ATTORNE"Patented Nov. 18, 1947 2,431,214 4LAMINATED STRUCTURE AND METHOD EugeneL. Vidal, New York, N. Y., and Laurence J. Marhoefer, Haddon Heights, N.J., assignors to Vidal Corporation, Camden, N. J., a corporation ofDelaware Application November 11, 1943, Serial No. 509,845, which is adivision of application Serial No. 356,426, September 12, 1940. Dividedand this application May 15, 1945, Serial No. 593,840

4 Claims.

This invention relates to structures fabricated from laminations ofadhesively treated material and to methods of making such structures.

An object of the invention is to provide a novel method for eliminatingsurface irregularities in a reinforced molded structure withoutdecreasing the strength of said structure.

Another object of the invention is to provide a process for making anovel laminated air foil having reinforcing members novelly secured tothe skin thereof.

Another object is to form in a novel manner the framework and skin of anairfoil or similar structure.

Another object is to produce an improved, reinforced molded shellstructure having a smooth and regular outer surface.

Heretofore the fabrication of laminated structures on molds has resultedin the production of either ridges or hollows in the skin of thestructure due to irregularities in the thickness of the reinforcingmembers, which either fail to fill, or project beyond, the groovesprovided therefor. The difficulty of securing a smooth surface in thecompleted reinforced shell structure is enhanced by the fact that thereinforcing Amembers are usually of wood, or other material,compressible under the substantial uid pressure to which they, as wellas the overlying laminations, are subjected in the molding operation. Itis substantially impossible to make the reinforcing members of preciselythat thickness that will insure that, when molded, their upper surfaceshall be precisely flush with the surface of the mold, which heretoforehas been a condition precedent to securing a smooth faced shellstructure. It is obviously impracticable after molding to lll in anyhollow, and while, if a ridge exists, it is possible, by, for example,sandpapering, to smooth the surface to eliminate the ridge, this cannotbe done without decreasing the thickness of the laminated skin andthereby substantially decreasing the skin strength.

To overcome these difficulties, without decreasing the skin strength,the reinforcing member is made of such thickness, usually somewhatundersized, that, when molded, its upper surface will terminate slightlybelow the surface of the mold. Before molding, however, one or moreeXtra strips of laminated material are located in the top lamination ofthe main skin at each of the grooves containing reinforcing members, thestrips being of width equal to or slightly greater than the width of thegroove. As a result, when the structure is molded, although a hollow isproduced in the main skin of the structure, these extra laminations llthis hollow. This may produce a ridge on the outer surface of the moldedstructure, but any portion of the extra laminations that projects abovethe level of the main skin surface may thereupon be removed, forexample, by a, sandpapering machine, to level off the outer surface ofthe shell structure without decreasing the skin strength.

The above and other objects and novel features of this invention willmore fully appear from the following detailed description when thelatter is read in connection with the accompanying drawings. It is to beunderstood, however, that the drawings are for the purpose ofillustration only and are not intended as a definition of the limits ofthe invention, reference being primarily had for this latter purpose tothe appended claims.

In the drawings, wherein like reference characters refer to like partsthroughout the several Views;

Fig. 1 is a top plan View of an airplane wing fabricated according tothe method of the present invention;

Fig. 2 is a sectional view taken substantially along line 2 2 of Fig. 1;

Fig. 3 is a fragmentary sectional View of a reinforcing member locatedin a mold and the manner of superposing skin laminations on said moldover said member;

Fig, 4 is a View similar to Fig. 3, showing the above parts aftermolding;

Fig. 5 is a perspective view of a portion of a type of mold or form onwhich the central part of the wing of Fig. 1 may be fabricated; and

Fig. 6 is a perspective View showing the parts of the wing sectionassembled on the mold of Fig. 6.

The present application is a division of our copending applicationSerial No. 509,845, led November 11, 1943, Patent No. 2,394,730, grantedFebruary l2, 1946, which in turn was divided out of our originalapplication Serial No. 356,426, filed September 12, 1940, Patent No.2,348,316, granted May 9, 1944.

According t0 the novel method comprehended by the present invention, astructural member, such as an aircraft wing, is novelly formed in one ormore sections from a, plurality of adhesively treated laminations of amaterial such as wood veneer. The laminations are shaped and bondedtogether by a molding operation which preferably includes theapplication of heat and fluid pressure but which may be accomplished bythe application of pressure only. 'I'he molded sections are removed fromthe mold and joined together to form the complete wing structure eithermechanically or by a local molding carried out by mechanical presses.

The veneer sheets which are utilized to carry out the method have athickness which depends on the desired weight, thickness and structuralstrength of the member being formed therefrom. For example, when amember having a high strength-to-weight ratio is to be formed, thinsheets from 1/45 to 1/8 are used in a 'sufficient number of layers togive the requisite strength, whereas to form a thick structure requiringlittle shaping it is satisfactory to employ sheets having a thickness oflr" or more. In the fabrication of aircraft parts, such as wings, weightmust be maintained at a minimum and, accordingly, thin sheets are used.Furthermore, although solid strips could be used as reinforcing or framemembers, it is preferable first to form said strips and otherreinforcing members from veneer laminations, a plurality of saidmembers, wherever possible, being molded as a block by the same moldingmethod, from which block the members are sawed or otherwise removed.

The sheets of material are treated with a suitable adhesive, preferablyof the thermoplastic or thermosetting group, as, for example, polyvinylbutyral. It is also possible toemploy other adhesives, for example, ofthe type adapted to be set by chemical reaction and requiring theapplication of pressure only during molding, such as urea formaldehyde.

The adhesive is applied to the sheets, preferably in a sufficientquantity to impregnate and coat the same in any suitable manner, as, forexample, by being sprayed or painted thereon or by dipping the sheets inthe adhesive. After the adhesive is applied, the sheets are permitted toseason for several hours and then if more thorough impregnation andcoating are desired the application of the adhesive and the seasoningare repeated one or more times. In the fabrication of a structure havingcurved surfaces from sheets impregnated with a thermoplastic, it ispreferable to mix a plasticizer, such as dibutyl phthalate, with theadhesive in sufficient quantity to make the impregnated sheetssufficiently iiexible to enable them to conform substantially to thecurved surface, the quantity of plasticizer added to the thermoplasticvarying inversely as the radius of curvature of the shape into which theveneer sheets are to be formed.

An aircraft wing fabricated according to the novel method of the presentinvention is shown by way of illustration in Fig. l. Said wing comprisesa beam section 40 located intermediate the leading and trailing edges ofthe wing and extending longitudinally, i. e., in the direction of thewing span, for almost the entire length of said span, said beam sectionconstituting the main support for the wing. A leading edge or nosesection 4l is secured to the forward edge of beam section 4i! andtrailing, edge or tail sections 42 and 43 are secured to the rear edgeof said beam section, trailing edge section 42 having a flap 44 hingedthereon, and section 43 having an aileron 45 associated therewith. Aseparate tip section 45 is also provided and is adapted to be secured tothe end of beam section 4Q and to constitute the tip of the wing.

Beam section 4G is formed on a mold 4? (Fig. 5) provided with transverserecesses 48 located where reinforcing frames for the beam are desiredand longitudinal grooves or recesses 49 which intersect said transverserecesses and extend substantially the length of the beam, the spacing ofrecesses 48 and 49 and the length of the latter recesses beingdetermined by the desired strength and rigidity of the beam section. Themold 41 may be provided with rounded edges and is preferably formed inseveral parts in order to be readily removable from the structure moldedthereon. The mold is first rendered non-adhesive by being covered with anon-adhesive material, such as Cellophane or cellulose acetate, or withsheets of veneer that have the surfaces thereof in engagement with saidmold free of adhesive. Transverse grooves 48 are then lled with a pairof laminated U-shaped frame members 5l and 52, corner pieces 53 and sidepieces 54, said frame members being recessed so as to interlock withstrips 55 which are adapted to fill grooves 49 and which are alsorecessed. Indentations 50 at each edge of mold 41 are filled witharcuate strips 58 which preferably extend the length of said mold and afiller strip 59 to square oi the edges is provided at each of the moldedges being positioned over each of said arcuate strips. It ispreferable to provide a side reinforcing strip between each pair oftransverse frames and grooves 56 are provided for this purpose in orderto receive side pieces.

Thereafter, a plurality of adhesively treated sheets of veneer 60 aresuperposed on the four sides of mold 4l and are temporarily secured tothe mold by any suitable means, such as cleats or belts (not shown). Theaggregate thickness of the veneer layers may progressively diminishtoward the beam tip, i. e., some of the layers may terminate at apredetermined distance from the tip.

When the above-described structure is properly assembled on the mold inthe above-described manner and the exposed surfacesl are renderednon-adhesive, for example, by being coated with cellulose acetate, theassembly and the mold are subjected to a molding operation whichincludes the application of pressure whereby the laminations are causedto closely conform to the mold shape while the adhesive is actuated andcaused to set. This is preferably accomplished by inserting the mold andthe assembly thereon into a flexible, substantially impervious containerand then placing said container into a pressure chamber wherein saidcontainer is preferably subjected to iiuid pressure. The interior of thecontainer is in communication with the exterior of the chamber so thatthe pressure in the latter will exhaust said container and cause thewalls thereof to closely engage the laminations on the mold. Thepressure is preferably applied by introducing compressed air and/orsteam into the chamber, the steam or other heating medium bel ing usedwhen the laminations have been treated with thermoplastic orthermosetting adhesives and heat is desired for activating the adhesive.The pressure remains applied until the adhesive has set and then themold and the structure molded thereon are removed from the chamber andfrom the container.

Heretofore the fabrication of reinforced laminated structures on moldshas resulted in the production of either ridges or hollows in the skinof the structure due to the irregularities in the thickness of thereinforcing members which either fail to lill or project beyond thegrooves provided therefor. To overcome this defect without decreasingthe skin strength in the products of the present invention, it isproposed to locate one or more extra strips 62 (Figs. 3 and 4) oflaminated material over the top lamination at each of the groovescontaining reinforcing members and to use reinforcing members 55, etc.,which are somewhat undersized, said strips being of a widthsubstantially equal to or slightly greater than the Width of saidgrooves. As a result, when the structure is molded, although a hollow isprovided in the skin of the structure, this hollow is filled with theseextra laminations. The portion of the latter which projects beyond theskin surface is thereafter removed without decreasing the skin strengthand this removal can be readily accomplished, for example, by asand-papering machine.

There is thus provided a novel method and product wherein a smooth skinis provided on an airfoil wing or other laminated molded structure eventhough said wing is molded from laminations of adhesively treatedmaterials and is provided with adhesively secured reinforcing members.

The invention in its broader aspects is not limited to the specificprocess and steps and article of manufacture shown and described butdepartures may be made therefrom within the scope of the accompanyingclaims without departing from the principles of the invention andWithout sacrificing its chief advantages.

What is claimed is:

l. A method of producing a smooth surfaced unitary reinforced laminatedshell structure comprising providing a mold having a recess therein;positioning in said recess an adhesively treated reinforcing memberadapted after molding to terminate slightly below the surface of themold, positioning on the mold over said recess and member adhesivelytreated laminations adapted to constitute the shell of said structure,applying at least one strip of adhesively treated material, having awidth not less than that of the recess, to said laminations over saidrecess, molding the shell laminations, applied strip or strips andreinforcing member into a unitary reinforced laminated shell structure,and effecting such reduction in the thickness of the strip or strips asmay be necessary to make the outer surface thereof flush with theadjacent outer surface of the shell structure.

2. A method of forming a smooth surfaced reinforced shell structure on amold from laminations of adhesively treated material which includeslocating reinforcing members in the recesses provided therefor in themold, superposing laminations adapted to constitute the shell of saidstructure on said mold, positioning one or more strips of adhesivelytreated material on the shell laminations directly over each of saidreinforcing members, and subjecting the assembly on the mold to amolding whereby the skin laminations, strips and reinforcing members arebonded together, and removing the thickness of the strip or stripsprojecting beyond the surface of the shell.

3. A reinforced molded article including in combination an outer shellcomposed of a plurality of adhesively bonded laminae integrally unitedby compression, a reinforcing member adhesively bonded to a portion ofthe inner surface of said shell by compression, an indentation in theouter surface of said shell opposite that area of the inner surfacethereof which is in contact with said reinforcing member, saidindentation being formed by the compression uniting said shell andreinforcing member, and at least one additional lamina adhesivelyIbonded and molded into the outer surface of said indentation to ll sameand make the outer surface of the shell opposite said reinforcing memberush with the adjacent outer surface of the shell.

4. A reinforced molded article including in combination an outer shellcomposed of a plurality of adhesively bonded laminae integrally unitedlby compression, a reinforcing member adhesively bonded to a portion ofthe inner surface of said shell by compression, an indentation in theouter surface of said shell opposite that area of the inner surfacethereof which is in contact with said reinforcing member, saidindentation being formed by the compression uniting said shell andreinforcing member, and at least one additional lamina adhesively bondedand molded into the outer surface of said indentation to ll same, theouter surface of said additional lamina being cut away suiciently tomake same flush with the adjacent outer surface of the shell.

EUGENE L. VIDAL. LAURENCE J MARHOEFER.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,912,931 Clay June 6, 19332,276,004 Vidal Mar. 10, 1942

